In typical RF systems, ON and OFF switching of transmitted RF signal power is controlled in order to avoid spectral splatter of the transmitted RF signal into adjacent transmission channels. Typically, a process known as burst shaping is employed in order to control the switching transients. In traditional RF transmission systems, a detector circuit in conjunction with a feedback loop is used to control PA output power. However, this traditional system has transient response limitations, which affects an attack ramp and a decay ramp of the transmitted RF signal and also offers complications in calibration procedures.
A publication, entitled “An advanced controller for multi-band open loop power control mode RF power amplifier,” Microwave Engineering, July 2002, issued to Trauth et al., describes a scheme for regulating the PA output power by controlling supply voltage provided to the PA on the supply voltage rails. Trauth et al. describe the difficulty of controlling a fast PFET regulator as it operates in the triode region. A solution in this publication is proposed that precludes operation of the PFET in the triode region. The problem with not allowing operation of the PFET in the triode region, as described by Trauth et al., is that the PFET size has to be significantly increased in order to obtain the same DC low drop out voltage condition. Otherwise the available supply voltage provided by the PFET regulator to the PA is restricted. This restriction results in decreased power consumption efficiency of the combined PFET and PA circuit and is thus unacceptable.
A need therefore exists for a compact LDO PFET regulator that offers an operating efficiency that overcomes the limitations of the prior art when used in conjunction with a PA. It is therefore an object of the invention to provide a LDO PFET regulator that operates in the triode region.